AI agent skill · by @ciembor

Working Effectively With Legacy Code

Apply Michael Feathers-inspired legacy-code rules when changing hard-to-test code safely with characterization tests, seams, sprout methods, or wrap methods.

Archived 2026-10-23 · Source updated 2026-09-10 · License: MIT. Check the original repository for the latest version.

SKILL.md instructions

# Working Effectively with Legacy Code Skill

Use this skill when a task involves risky legacy changes, missing tests, characterization tests, seams, dependency breaking, sprout method, wrap method, or incremental risk reduction.

Before making design or code decisions, read and apply [working-effectively-with-legacy-code.mini.md](working-effectively-with-legacy-code.mini.md). Use [working-effectively-with-legacy-code.md](working-effectively-with-legacy-code.md) only as a deeper reference when the mini rules are not enough for the current legacy-code tradeoff.